1. Field of the Invention
The present invention relates to the detection of recent human presence, and, more specifically, to a method for detecting recent human presence in an environment using the rate of decay of carbon dioxide concentration levels within that environment.
2. Description of the Related Art
Real-time detection of human presence in an environment such as a home, car, or office can be advantageous for several reasons. Indeed, there are many systems that detect human presence in real-time, including lighting and ventilation systems, in order to reduce energy consumption and costs or to improve the quality of the air within the space. These systems use a variety of means to detect human presence in real-time, including sensor technologies such as gas concentration sensors, infrared detectors, seismic detectors, and other human presence detectors. In limited applications, these systems can also quantify the real-time human presence by determining the number of humans that are present in a space.
However, these systems are not capable of either detecting recent human presence once the space no longer has a human present or quantifying recent human presence once the space no longer has a human present. Once the environment or space is empty the sensor is no longer activated and is thus unable to determine human presence. Further, these systems are not able to function in a space or environment that is not already configured to contain a sensor. In other words, the human presence cannot be detected unless the sensor was in the room at the same time as the human beings.
However, human presence will typically leave behind signatures that can be detected and analyzed. Additionally, measurements of some signatures can be quantitative such that the amount of recent human presence can be determined. Thus, there is a need for methods and systems that detect and/or quantify recent human presence.